tree translates to Pod::Simple::SimpleTree, and the tree root is what's returned. This is what you want to use if you want to create your own formatter.

htMl translates to Pod::Simple::HTML. When dealing with htMl, the 3rd and 4th arguments are is used to prefix all non-local L<>inks, by temporarily overriding *Pod::Simple::HTML::do_pod_link. and *Pod::Simple::HTML::do_man_link. pod_link_prefix is "?" by default. man_link_prefix is http://man.linuxquestions.org/index.php?type=2&query= by default. The prefix always gets html escaped by Pod::Simple. An example man link is crontab(5).